1. Field of the Invention
The present invention generally relates to an optical light guide member and, more particularly, to the light guide member for guiding a beam of light from a light emitting element, fixedly mounted on a printed circuit board, towards a display window defined in a casing that encloses the light emitting element and the printed circuit board therein. The present invention also relates to an optical light guide assembly comprising a plurality of the optical light guide members connected together in a juxtaposed fashion.
2. Description of the Prior Art
It has long been well known that a transparent rod made of a transparent plastic material such as an acrylic resin can be used as an optical light guide for guiding a beam of light therethrough. Although incapable of being used in a long-distance light transmission such as accomplished by an optical glass fiber, the transparent rod is often used to guide a beam of light, emitted by a light emitting element such as, for example, a light emitting diode to any desired location.
By way of example, an electronic appliance such as a controller makes use of at least one light emitting diode as a status indicator to provide a visual indication of, for example, whether or not the electronic appliance is properly operated. Depending on the type of the electronic appliance and/or the type of the light emitting diode, the light emitting diode is often fixedly positioned on a printed circuit board and an indicator window is defined in a casing that encloses the printed circuit board therein. Where there is a substantial distance between the light emitting diode on the printed circuit board and the indicator window in the casing, the transparent light guide rod is generally employed for guiding a beam of light from the light emitting element to the indicator window so that a user or attendant worker can ascertain whether or not the light emitting diode is electrically energized, by looking at the indicator window.
The Japanese Laid-open Utility Model Publication No. 4-81101, published Jul. 15, 1992, discloses the use of a generally rectangular LED plate lens formed integrally with a plurality of generally cylindrical independent light guide bosses protruding outwardly from one surface of the LED plate lens. The LED plate lens is fixed to an inner surface of a lower front panel portion of a television receiver cabinet, where indicator windows are formed, so that respective free ends of the light guide bosses can be aligned with light emitting diodes that are fixedly mounted on a printed circuit board within the television receiver cabinet. This publication describes that each light guide boss may have a tubular shape and may be inclined so as to optically connect the respective light emitting diode with the associated indicator window where the indicator windows and the light emitting diodes are displaced in level relative to each other.
The Japanese Laid-open Patent Publication No. 7-230024, published Aug. 29, 1995, discloses, in one embodiment, a generally triangular light guide member made of a transparent plastic material and having first and second surfaces lying perpendicular to each other and a third surface lying at an angles relative to any one of the first and second surfaces. While the first and second surfaces of the light guide block are used as light receiving and emitting faces, respectively, the third surface is used as a reflecting surface for reflecting a beam of light, which has entered the light guide block through the light receiving face, towards the light emitting face.
This publication also discloses, in another embodiment, a monolithic light guide member made of a transparent plastic material and having first, second and third reflecting surfaces defined therein along the length thereof. The light guide member according to the alternative embodiment disclosed in this publication is so designed that a beam of light emitted from the light emitting diode and entering the light guide member through the light receiving face is, after having travelled along a first path, first reflected by the first reflecting surface so as to travel along a second path, then reflected by the second reflecting surface so as to travel towards the third reflecting surface along a third path in a direction substantially counter to the direction of travel of the beam towards the first reflecting surface, and finally reflected by the third reflecting surface so as to travel along a fourth path towards the indicator window in a direction substantially parallel to the direction of travel of the beam along the second path. The first to third paths defined in the light guide means lie in a single common plane substantially perpendicular to the printed circuit board.
The Japanese Laid-open Patent Publication No. 8-184713, published Jul. 16, 1996, discloses a monolithic light guide member of a generally L-shaped plate-like configuration made of a transparent plastic material and including long and short bodies angled relative to each other. The light guide member disclosed in this publication is used in a notebook-sized personal computer as a status indicator and is so designed and so configured that a beam of light emitted from a light emitting diode can be viewed from two directions generally perpendicular to each other regardless of whether a lid is closed or whether the lid is opened. For this purpose, the light guide member has, in addition to a single light receiving face aligned with the light emitting diode, first and second light emitting faces and is so designed that, regardless of the position of the lid, a beam of light from the light emitting element can travel directly towards the first light emitting face, but towards the second light emitting face after having been reflected by a series of four reflecting faces or can, alternatively, travel simultaneously towards the first and second light emitting faces after having been scattered by a roughened reflecting face.
According to any one of the foregoing publications, regardless of the number of reflections taking place in the light guide block or member, the beam of light travelling from the light receiving face towards the light emitting face or faces propagates in a single plane lying at an angle or right angles relative to the printed circuit board.
A certain encased electric appliance such as, for example, a sequence controller requires the use of a plurality of light emitting diodes to provide a visual indication of not only different operating statuses of the electric appliance, but also different line statuses of lines leading to and from the circuitry. Where the circuit design is given according to standards, for example, VDEO 160: 1988 (prEN50178: 1995) or EN61131-2: 1995, downscaling of the sequence controller is difficult to achieve because of a substantial distance found between the position of the light emitting diodes, mounted on the printed circuit board, and that of the indicator windows defined in a wall of the casing.
More specifically, the sequence controller includes relatively bulky electric component parts and relatively small electric component parts, both mounted on a printed circuit. The relatively bulky electric component parts include at least one modular pin connector having a row of a plurality of connector pins, a plurality of relay switches, and a transformer, all mounted on a primary circuit region (a high-voltage active region) of the printed circuit board whereas the relatively small electric component parts including the light emitting diodes are mounted on a secondary circuit region (a low-voltage active region) of the printed circuit board. The primary and secondary circuit regions are required to have a space of insulation of, for example, about 3 mm.
On the other hand, some or all of the indicator windows in the casing of the sequence controller discussed above must be coordinated with respective positions of the connector pins in the modular pin connector so that statuses of the lines associated with those connector pins can be visually displayed. This means that the primary circuit region in the printed circuit board must be positioned adjacent to the wall where the indicator windows are defined and the modular connector is installed and that the light emitting diodes included in the secondary circuit region have to be positioned in at least one row at a location distant from the indicator windows.
One possible solution to accomplishing the downscaling of the sequence controller would be the use of elongated light guide members one for each light emitting diode to convey a beam of light from the respective light emitting diode towards the associated indicator window. Each of these elongated light guide members may be of a design substantially similar to or identical with the light guide member disclosed in any one of the previous discussed publications.
However, as discussed hereinbefore, in the prior art light guide member or block referred to hereinbefore, the beam of light entering the light guide member or block travels only in one common plane at right angles to the printed circuit board. Accordingly, when the prior art light guide members are used in the sequence controller of the type discussed above, the light emitting diodes have to be positioned spaced a substantial distance from each other, thus limiting the extent to which the sequence controller can be downscaled.
The use of an optical glass fiber may be contemplated in place of the plastic light guide member. However, it has been found that where the space available between the printed circuit board and a panel of the casing is extremely limited, the optical glass fiber cannot be conveniently employed since it cannot be bent at right angles. Bending the optical glass fiber at right angles or an acute angle without allowing it to break upon bending requires a substantial radius of curvature and, hence, a relatively large space is required to accommodate the optical glass fiber, which in turn hampers the downscaling of the electronic appliance.